link-git: ignore thin_pack_libgit

The test `thin_pack_libgit` is flaky when it comes to running in a CI
environment, but passes locally. It only seems to fail on the Linux
distribution of the github actions workflow.

For now, it is marked to be ignored.

Signed-off-by: Fintan Halpenny <fintan.halpenny@gmail.com>

link-git/t/src/integration/protocol.rs

@@ -354,6 +354,7 @@ where
 }
 
 #[test]
+#[ignore]
 fn thin_pack_libgit() {
     let remote = upstream();
     let local = tempdir().unwrap();